The long term objective of these research efforts is to develop a diagnostic test for Prader-Willi syndrome (PWS) based on saliva. PWS is a genetic disorder characterized by psychomotor and growth retardation, infantile hypotonia, characteristic facies, small hands and feet, and early onset of childhood hyperphagia with consequent obesity. Abnormal saliva has been a consistent finding in these individuals. An interstitial deletion of bands q11.2-q13 of the paternally derived chromosome 15 has been found in 70% of PWS patients. The majority of non- deletion PWS patients exhibit material disomy for chromosome 15, further demonstrating that loss of paternal alleles is responsible for the phenotype of PWS. The goal of these proposed studies is to determine what is abnormal about the saliva in these patients and to evaluate saliva's usefulness as a diagnostic sign of PWS. The Specific Aims of this proposal are l) To perform compositional studies on saliva from individuals with PWS and 2) To relate the underlying genetic defect in PWS patients to the salivary composition. Specific Aim l will be accomplished by the measurement of the concentrations of fluoride and chloride by ion specific electrode, of calcium and sodium by atomic absorption, and of phosphorus and total protein by spectrophotometric determination. The protein composition will be assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. If specific alterations of salivary components, such as calcium and phosphate concentrations, are found in the PWS individuals, these alterations could be used as a diagnostic test for early identification of PWS. This may be particularly valuable for females and African Americans who are at risk for remaining undiagnosed. It may also provide data regarding the mechanism of decreased salivary flow in these patients. Specific Aim 2 will be accomplished by a combination of cytogenetic (high resolution banding and fluorescence in situ hybridization) and molecular (methylation studies and the PCR-based CA dinucleotide repeat assay) techniques in order to determine the underlying genetic defect (deletion, uniparental disomy, or apparently normal constitution) in these patients. The comparison of the genetic defects will indicate alterations in salivary composition can be used to aid in the diagnosis of all subtypes of PWS. The understanding of altered salivary secretion in these individuals will lead to a better comprehension of normal saliva secretion and of secretion in general.